1. Field of the Invention
The present invention relates to a memory array, and in particular to an area saving electrically-erasable-programmable read-only memory (EEPROM) array.
2. The Prior Arts
Presently, in the semiconductor industry, Complementary Metal Oxide Semiconductor (CMOS) manufacturing process has become an ordinary manufacturing method for Application Specific Integrated Circuit (ASIC). With the rapid progress and development of the computer and information industries, Flash memory and electrically-erasable-programmable read-only memory (EEPROM) have been widely utilized in various electronic products for its non-volatile memory capability of being electrically programmable and erasable, such that data stored therein will not be lost, even when its power supply is turned off.
In general, a non-volatile memory is programmable, and the memory stores charges in order to change the gate voltage of a transistor in the memory, or the memory will not store charges, such that the gate voltage remains unchanged as the original gate voltage of the transistor in the memory. For an erasure operation, the charges stored in the non-volatile memory are removed, such that the gate voltage of the transistor in the memory will return to its original value. Refer to FIGS. 1 & 2 for a circuit diagram of a non-volatile memory according to the prior art, and a circuit diagram of a non-volatile memory layout according to the prior art respectively. As shown in FIGS. 1 & 2, the non-volatile memory is composed of a plurality of memory cells. Wherein, each memory cell includes a transistor 10 and a capacitor 12, between two adjacent byte-memory cells is provided with two bit lines BL1 and BL2, such that the area occupied is increased. Moreover, refer to FIG. 3 for a cross section view of a memory cell of a non-volatile memory according to the prior art, as shown in FIG. 3, the capacitor 12 is located at one side of the transistor 10, since this kind of structure occupies large area, it will further raise the cost.
Therefore, presently, the area occupied by the memory cells of a non-volatile memory is rather large, and it has much room for improvement.